A convenient access to: N -phosphonio-substituted NHC metal complexes [M = Ag(i), Rh(i), Pd(II)]

Article abstract of DOI:10.1039/c7dt02759a

A series of NHC pre-ligands featuring a pendant phosphonium moiety attached to N′ position through a propyl linker was readily obtained upon quaternization of N-mesityl- and N-methyl-imidazole, or N-mesityl-imidazoline using (3-bromo-propyl)-triphenylphosphonium bromide. Reactions of the resulting dicationic salts with [PdCl(allyl)]₂ in the presence of K₂CO₃ afforded the anticipated NHC-ligated Pd(ii) metal complexes in high yields. Further treatment of the latter complexes with tBuOK induced a deprotonation of the carbon atom adjacent to the phosphonium moiety and the formation of the corresponding C,C-chelating NHC-phosphonium ylide Pd(ii) complexes. Investigation of an alternative synthetic route involving a silver transmetallation reaction incidentally allowed isolation and full characterization of an unusual dimeric tetranuclear NHC Ag(i) complex of general formula [(NHC～P⁺)₂(Ag₄Br₆)^2-].

Full text of DOI:10.1039/c7dt02759a

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DOI: 10.1039/C7DT02759A
A Convenient Access to N-Phosphonio-Substituted NHC Metal Complexes
M = Ag(I), Rh(I), Pd(II)]
[
Idir Benaissa, Rachid Taakili, Noël Lugan, Yves Canac*
LCC-CNRS, Université de Toulouse, INPT, UPS, 205 route de Narbonne 31077 Toulouse
Cedex 4, France
E-mail: yves.canac@lcc-toulouse.fr
31
1
1
13
1
Electronic supplementary information (ESI) available: P{ H}, H, and C{ H} NMR
spectra for all new compounds.
Abstract
A series of NHC pre-ligands featuring a pendant phosphonium moiety attached to N’ position
through a propyl linker was readily obtained upon quaternization of N-mesityl- and N-methyl-
imidazole, or N-mesityl-imidazoline using (3-bromo-propyl)-triphenylphosphonium bromide.
2 2 3
Reactions of the resulting dicationic salts with [PdCl(allyl)] in the presence of K CO
afforded the anticipated NHC-ligated Pd(II) metal complexes in high yields. Further treatment
of the latter complexes with tBuOK induced a deprotonation of the carbon atom adjacent to
the phosphonium moiety and the formation of the corresponding C,C-chelating NHC-
phosphonium ylide Pd(II) complexes. Investigation of an alternative synthetic route involving
a silver transmetallation reaction incidentally allowed isolation and full characterization of an
+
2-
unusual dimeric tetranuclear NHC Ag(I) complex of general formula [(NHC~P )
2
(Ag
4
Br
6
) ].
Keywords: Electrostatic effect, NHC, phosphonium, silver, palladium, ylide.
1

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Introduction
1
Following the initial report of stable N-heterocyclic carbenes (NHCs), their
2
functionalization became rapidly a hot topic because of their immediate applications in the
field of organometallic chemistry, functional materials and homogeneous catalysis.
The introduction of a phosphine moiety onto the NHC framework allowed the development of
a large variety of heteroleptic systems, whose intrinsic properties are somewhat related to the
3
position of the P-substituent. The P-center can formally replace or cooperate with the
carbenic center - C-2 position -, depending on whether the phosphine is directly attached to
the C-2 atom or located at the remaining - C-4/5 and N - positions of the heterocycle. The
association leads respectively to the formation of an electron-poor imidazoliophosphine better
4
described as a NHC-phosphenium adduct with residual donor ability, or to a phosphino-
5
imidazolium salt, which may act as a P,C-bidentate ligand upon deprotonation.
6
Phosphorus can also be introduced on the NHC moiety as a phosphonium moiety,
resulting in the formation of a phosphonio-imidazolium salt, which would thus be dicationic
7
8
in nature. Based on more exemplified cationic phosphines, the presence of a positive charge
on the NHC backbone, regardless of its position, is expected to modulate to some extent the
physico-chemical properties of the system. If located in close proximity of the carbenic
9
center, the positive charge can also influence the electronic properties, where a decrease in
the donating character is anticipated, as was recently confirmed by the report of a 5-
6c
phosphonio-substituted NHC ligand. Another benefit of the positive charge is related to the
1
0
possibility of converting phosphoniums into phosphonium ylides. This close relation was
first illustrated with the 2-triphenylphosphonio-substituted imidazolidinium salt A, which
gives an unstable C-amino phosphonium ylide upon a two-electron reduction, and finally
6a
fragments into carbene and triphenylphosphine (Scheme 1, up). As well, the deprotonation
+
of the pendant P −Me substituent in N-phosphonio-substituted NHC metal complexes B of
+
-
+
general formula [(o-C
6 4 2
H AB) M, X , with A = NHC, B = Ph P Me, M = Pd(allyl)Cl,
Rh(cod)Cl, X = OTf] led to the corresponding C,C-chelating NHC-phosphonium ylide
1
1
complexes (Scheme 1, down). Precedents for such systems include a π-allyl Pd(II) complex
11a
2
that catalyzes allylic substitutions, and a series of Rh(CO) complexes that demonstrate the
12
stronger donating character of phosphonium ylides vs NHC ligands.
2

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Scheme 1. Influence of the position of the phosphonium group on the NHC backbone,
6
a
11-
introduced either at the carbenic center (up) or in remote position from the carbenic center
1
2
(down).
Due to their intriguing properties but also promising applications, a convenient access to
NHC ligands bearing a phosphonium moiety and the study of their coordinating behavior
towards various metal centers deserve to be developed.
Results and discussion
1
3
Treatment of 1-(2,4,6-trimethylphenyl)-imidazole
triphenylphosphonium bromide in C Cl at 130 °C afforded the 1-mesityl-3-(3-
triphenylphosphonio) propyl)-imidazolium bromide [1]Br in 84 % yield (Scheme 2). Similar
reactivity pattern could be also obtained from 1-methyl-imidazole 2, and 4,5-dihydro-1-
1
with (3-bromo-propyl)-
6
H
5
(
2
1
4
(
2,4,6-trimethylphenyl)-imidazole 3, allowing the corresponding N-phosphonio-substituted
imidazolium salts [2]Br , and [3]Br to be isolated in 97 and 74 % yield, respectively.
Structural diversity could be also provided by the phosphonium salt, as examplified with the
formation of the 1-mesityl-3-(3-(triphenylphosphonio) ethyl)-imidazolium bromide [1’]Br
obtained in 84 % yield upon reaction of 1 with (2-bromo-ethyl) triphenylphosphonium
bromide in CH CN at 80 °C (Scheme 2). Given the poor solubility of the salts [1-3]Br in
common polar solvents, a metathesis reaction was carried out with NaOTf in CH CN,
affording the corresponding dicationic salts [1-3](OTf) in good yields (ca. 84-97 %; Scheme
).
2
2
2
,
3
2
3
2
2
3

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+
Scheme 2. Preparation of N-[(CH
2
)
n
PPh
3
] (n = 2, 3) substituted imidazolium salts [1-3]X
2
(X
=
Br, OTf) from their azole precursors 1-3.
3
1
2 P
The P NMR spectrum of [1-3]X (X = Br, OTf) displayed a singlet at ca. δ +21.0-24.8
15
ppm, in the typical range for phosphonium derivatives. The imidazolium protons were
1
evidenced by a characteristic low field signal at ca.
The structures of imidazolium salts [1]X (X = Br, OTf)
unambiguously confirmed by X-ray diffraction analysis of single crystals (Figure 1).
δ
H
+8.2-10.2 ppm in the H NMR spectra.
2
, 2 2
[2](OTf) , and [3]Br were
1
6
Figure 1. Perspective views of the cationic part of N-phosphonio-derived imidazolium salts
1]Br (left), [2](OTf) (middle), and [3]Br (right) with thermal ellipsoids drawn at the 30 %
probability level. Selected bond lengths [Å] and angles [°]: [1]Br : C1−N1 = 1.332(3); C1−N2
: C1−N1 = 1.326(5); C1−N2
: C1−N1 = 1.305(3); C1−N2 =
[
2
2
2
2
=
1.329(3); C2−C3 = 1.353(3); N1−C1−N2 = 108.5(2). [2](OTf)
1.328(3); C2−C3 = 1.348(5); N1−C1−N2 = 109.0(3). [3]Br
.306(2); C2−C3 = 1.528(4); N1−C1−N2 = 114.0(2).
2
=
2
1
The dications [1-3]X
2
complement the undeveloped family of phosphonio-imidazolium
whose coordination properties deserve to be investigated. For this purpose, a
values of
20-24 in DMSO). Disappointingly, addition of a weak base
to the ethylene bridged salt [1’]Br led to the quantitative recovery of
6
,11
salts
sequential complexation strategy was first selected despite the similarity of the pK
a
1
7
the two cationic moieties (pK
such as Ag O or K CO
a
2
2
3
2
the imidazole 1 along with the vinyl phosphonium salt [4]Br (Scheme 3), whatever the
conditions of the reaction, solvent, temperature, stoichiometry, presence of a metal precursor
P
or not. The structure of [4]Br was deduced from the presence of a singlet at δ +19.4 ppm in
4

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31
1
the P NMR spectrum, and a ABCX type system spread over the +6.2-7.5 ppm zone in the H
1
8
NMR spectrum. An E
2
type mechanism wherein the 1-mesityl-imidazole substituent
behaves as a leaving group can rationalize the formation of phosphonium [4]Br.
Scheme 3. Formation of 1-(2,4,6-trimethylphenyl)-imidazole
triphenylphosphonium salt [4]Br from the ethylene bridged imidazolium salt [1’]Br
presence of a weak base (using the K CO base, [4]Br was isolated in 91 % yield).
1
and vinyl
2
in the
2
3
In contrast, the presence of a propyl bridge prevented any elimination reaction, and
treatment of [1]Br with anhydrous K CO in the presence of half an equivalent of
RhCl(cod)] or [PdCl(allyl)] in CH CN, led to the targeted N-phosphonio-substituted NHC
2
2
3
[
2
2
3
metal complexes [5-6]Br in 93-95 % yield (Scheme 4). The formation of these cationic NHC
1
complexes was first evidenced by the disappearance of the characteristic H signal of the
3
1
imidazolium proton of the precursor [1]Br
2
. In the P NMR spectrum, no significant change
was observed between the P resonance of the complexes and that of [1]Br ([1]Br +24.2
ppm; [5]Br: +24.0 ppm; [6]Br: +23.9 ppm) indicating that the phosphonium moiety
remained essentially unchanged. In C NMR spectra, the N
[5]Br: +182.1 ppm; [6]Br: +180.9 ppm) was found to be strongly deshielded with
respect to the N CH carbon atom of [1]Br
the N
3
1
2
2 P
: δ
δ
P
δ
1
P
3
2
C carbon atom of complexes
(
δ
C
δ
C
2
2
(δ
C
+139.6 ppm). For [5]Br, the coordination of
1
2
C center to the metal was also supported by the JCRh coupling constant of 50.9 Hz.
The structure of [5]Br was established from the X-ray diffraction analysis of single yellow
16
crystals grown from a CH
3 2
CN/Et O mixture (Figure 2). The Rh(I) atom resides in a square-
planar environment, where the NHC ring is quasi-orthogonal to the Rh coordination plane
(dihedral angle N2−C1−Rh1−Br1: 80.46°). The C1−Rh1 (2.028(2) Å) bond distance is within
6c,12a
the range of those reported for related cationic NHC Rh(I) complexes.
In the case of
+
[
6]Br, the existence of a Pd−Br bond was assessed by ESI mass spectroscopy (m/z: 717 [M] ).
5

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Scheme 4. Access to the N-phosphonio-NHC Rh(I), and Pd(II) complexes [5-6]Br from the
salt [1]Br , via the deprotonation route.
2
To anticipate Cl/Br metal exchanges as observed in complexes [5-6]Br, N-phosphonio
imidazolium salts [1-3](OTf) were then considered for coordination purposes. Treatment of
1-3](OTf) with half an equivalent of [PdCl(allyl)] in CH CN in the presence of anhydrous
CO
2
[
2
2
3
K
2
3
afforded the cationic NHC Pd(II) complexes [6-8](OTf) in 87-93 % yields (Scheme
1
5
). Coordination of the carbenic center was evidenced by the absence of the characteristic H
31
NMR imidazolium signal. The selectivity of the reaction was assessed by P NMR
1
5
spectroscopy showing only phosphonium resonances (ca.
stereoisomers of 7 were formed in a 55/45 ratio, whose origin could be the result of a
restricted rotation around the N C−Pd bond, as already noticed in a related Pd(II) complex of
a N-methylated imidazolin-2-ylidene ligand.
The structure of [6](OTf) was confirmed by X-ray diffraction analysis of single crystals
P
δ +23.8-24.2 ppm). Two
2
1
1a
16
2 2 2
obtained from CH Cl /Et O mixture (Figure 2). The Pd(II) atom resides in a quasi-square-
planar environment where the coordination plane defined by the C1, C7, C9, and Cl1 atoms is
positioned nearly orthogonally to the NHC ring (dihedral angle N1−C1−Pd1−Cl1: 67.84°).
2
The N C−Pd bond distance (C1−Pd1 = 2.040(2) Å) is similar to those reported in cationic
11a
NHC Pd(II) complexes. As observed for Rh(I) complex [5]Br, the halogen atom and the
phosphonium moiety are arranged on the same side of the carbenic ring.
6

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Scheme 5. Access to the N-phosphonio-NHC Pd(II) complexes [6-8](OTf) from the salts [1-
](OTf) , via the deprotonation route.
3
2
Figure 2. Perspective views of the cationic part of N-phosphonio-NHC metal complexes
5]Br (left), and [6](OTf) (right), with thermal ellipsoids drawn at the 30 % probability level.
[
Selected bond lengths [Å] and angles [°]: [5]Br: C1−N1 = 1.364(2); C1−N2 = 1.357(3);
C1−Rh1 = 2.028(2); Rh1−Br1 = 2.4883(5); N1−C1−N2 = 103.9(1); N1−C1−Rh1 = 131.6(1);
N2−C1−Rh1 = 124.6(1); C1−Rh1−Br1 = 90.95(5). [6](OTf): C1−N1 = 1.360(2); C1−N2 =
1.355(3); C1−Pd1 = 2.040(2); C7−Pd1 = 2.190(2); C8a−Pd1 = 2.106(6); C9−Pd1 = 2.113(3);
Pd1−Cl1 = 2.3921(7); N1−C1−N2 = 104.0(2); N1−C1−Pd1 = 127.1(1); N2−C1−Pd1 =
1
28.3(2); C1−Pd1−Cl1 = 91.76(6).
An alternative route involving the transmetallation of a NHC Ag(I) complex was also
2 2 2 2 2
investigated from [1]Br . Addition of Ag O to a solution of [1]Br in CH Cl in the presence
1
9
of molecular sieves led to the formation of complex 9, isolated in 60 % yield (Scheme 6). As
31
observed for NHC complexes [5-6]X, the P NMR resonance underwent little change upon
13
coordination of the NHC moiety ([1]Br
2
:
δ
P
+24.2 ppm; 9:
P
δ +23.7 ppm). The C NMR
signal of the N C center of 9 (δC +181.1 ppm) was found in the typical range of carbenic
2
6
c,9
carbon atoms in cationic NHC Ag(I) complexes.
with the formation of a dicationic [(
These data would be consistent either
+
ꢀ
-Br) Ag (NHC~P ) ] complex, or a tricationic
2
2
2
+
+
[
Ag (NHC~P ) ] complex, which stand as the most classically observed arrangements in
2
7

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2
0
NHC Ag(I) complexes. The structure of 9 could be finally determined by X-ray diffraction
1
6
2 2 2
analysis of colorless crystals grown from a CH Cl /Et O mixture (Figure 3).
Scheme 6. (a) Access to the N-phosphonio-NHC Ag(I) complex 9 from [1]Br
2
, and to the
corresponding Rh(I), and Pd(II) complexes [5-6]Br, via the transmetallation route. (b)
2
Formation of the N-phosphine oxide-NHC Ag(I) complex 10 from [1]Br , in the absence of
molecular sieves.
Surprisingly enough, the XRD analysis revealed a totally different picture, the complex 9
being not only dimeric, but also tetranuclear. The latter is indeed based on a centrosymmetric
2−
(Ag
4
Br
6
)
core acting as a structuring bridge between two head-to-tail phosphonio-NHC
2
−
ligands. Through a reduction of the +/- charge separation, the (Ag
4
Br
6
)
anion screens the
trans-coordinated cationic NHC ligands, thus minimizing the repulsive electrostatic
interaction between the two positives charges. The resulting zwitterionic structure induces a
specific electrostatic arrangement in the solid state, certainly at the origin of the overall
2
1
cohesion of the edifice. The oxidation state of the Ag atoms is formally +1, with the two
i
negative charges delocalized over the metallic fragment. The peripheral Ag1 and Ag1 atoms
coordinated by two
ꢀ
2
-Br ions and the carbenic center, reside in a distorted trigonal
i
environment, while the central Ag2 and Ag2 atoms coordinated by four
2
ꢀ -Br ions present a
distorted tetrahedral configuration. The Ag−Br bond distances (Ag−Br = 2.610(4)-2.790(3)
21
Å) fall in the range of bridging Ag−Br distances. The relative positioning of the Ag and Br
2 2
atoms results in the formation of three adjacent Ag Br four-membered rings, where the
8

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central cycle is quasi-planar and the two side ones adopt a butterfly type-conformation. The
i
i
Ag1−C1/Ag1 −C1 bond distances (2.127(2) Å) are comparable to those described in related
NHC Ag(I) complexes, especially with those reported in the 5-phosphonio-derived NHC
6
c
(
Ag−Cav = 2.139 Å). Complex 9 exhibits close Ag--Ag contact between two Ag atoms of
different coordination number (Ag1--Ag2 = 2.9867(4) Å), thereby suggesting the presence of
1
0
10
22
significant close shell d --d argentophilic interactions. Although larger than a single
Ag−Ag bond (e.g. 2.53 Å in Ag ), the Ag1--Ag2 distance is indeed shorter than twice the van
der Waals radii of the corresponding Ag atoms (3.44 Å). Despite tremendous structural
2
20
diversity of [(NHC)AgX] type-complexes described over the years, the architecture
observed in complex 9, dictated by an interplay of electrostatic and steric effects is unique,
thanks to the preparation of a novel type of N-phosphonio-substituted NHC ligand.
2 2
It is worth noting that treatment of [1]Br with Ag O in the absence of molecular sieves led
to a different reactivity, allowing complex 10 to be isolated in 90 % yield (Scheme 6). As
1
observed for 9, H NMR spectroscopy indicated the disappearance of the imidazolium proton.
31
The P NMR spectrum displayed a singlet at
δ
P
+29.7 ppm, slightly downshifted with respect
15
to standard phosphonium values. The structure of 10 was finally established by X-ray
16
diffraction analysis of a single crystal grown from a CH
geometry is based on a centrosymmetric arrangement featuring a Ag
intercalated between two head-to-tail NHC ligands. The angular deviation between the mean
planes of the Ag Br nucleus and the NHC ring is about 34.03°. The Ag--Ag distance
3.8790(5) Å) greater than the sum of the corresponding van der Waals radii (3.44 Å)
2
Cl
2
/Et
2
O mixture (Figure 4). The
2
(ꢀ
-Br) central core,
2
2
2
(
precludes any significant argentophilic interaction. The structure reveals also the presence of
diphenylphosphine oxide extremities which formally results from the hydrolytic oxidation of
the phosphonium moities. During the transmetallation, the basic conditions due to the
formation of H
conversion of [1]Br
Br) Ag (NHC~P(O)Ph ]-type structure of complex 10 emphasizes the role of the positive
2
2
O in the presence of Ag O (an excess is indeed required to obtain total
2
3
2
)
can explain the observed reactivity.
The [(ꢀ-
2
2
2 2
)
charges of the phosphoniums in the unconventional arrangement obtained for the complex 9.
9

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i
Figure 3. Perspective view of NHC Ag(I) complex 9 (30 % probability ellipsoids; = 1−x, −y,
1−z). Selected bond lengths [Å] and angles [°]: C1−N1 = 1.355(3); C1−N2 = 1.355(3);
C1−Ag1 = 2.127(2); Ag1−Br1 = 2.7246(3); Ag1−Br2 = 2.7148(4); Ag2−Br1 = 2.6660(4);
i
…
Ag2−Br2 = 2.7032(4); Ag2−Br3 = 2.6100(4); Ag2−Br3 = 2.7900(3); Ag1 Ag2 = 2.9867(4);
N1−C1−N2 = 103.8(2); N1−C1−Ag1 = 127.2(1); N2−C1−Ag1 = 129.0(1); C1−Ag1−Br1 =
1
24.64(6); C1−Ag1−Br2 = 135.03(6); Br1−Ag1−Br2 = 97.87(1); Br1−Ag2−Br2 = 99.60(1);
i
Br1−Ag2−Br3 = 119.33(1); Br2−Ag2−Br3 = 128.67(1); Br1−Ag2−Br3 = 103.91(1);
i
i
Br2−Ag2−Br3 = 99.60(1); Br3−Ag2−Br3 = 101.70(1).
Figure 4. Perspective view of NHC Ag(I) complex 10 with thermal ellipsoids drawn at the 30
i
%
probability level; = −x, −1−y, 2−z). Selected bond lengths [Å] and angles [°]: C1−N1 =
1
.358(5); C1−N2 = 1.350(4); P1−O1 = 1.494(3); C1−Ag1 = 2.101(3); Ag1−Br1 = 2.4818(5);
…
i
Ag1 Ag = 3.8790(5); N1−C1−N2 = 103.9(3); N1−C1−Ag1 = 126.7(3); N2−C1−Ag1 =
i
i
1
29.4(3); C1−Ag1−Br1 = 162.4(1); C1−Ag1−Br1 = 108.7(1); Br1−Ag1−Br1 = 88.84(5).
1
0

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Beyond its fascinating structure, the question was whether the Ag complex 9 could be used
20
as a carbene transfer agent, as are more conventional NHC Ag(I) complexes. In that
prospect, 9 was reacted with a stoichiometric amount of [RhCl(cod)] and [PdCl(allyl)] in
CH Cl2. Gratifingly, this led to the formation of corresponding cationic NHC metal complexes
5]Br, and [6]Br, isolated in 87 %, and 88 % yield, respectively (Scheme 6). From [1]Br2, N-
2
2
2
[
phosphonio NHC metal complexes [5-6]Br were thus obtained in 93-95 % yields using the
one-step deprotonation method (Scheme 4), while the two-step transmetallation strategy
allowed the same complexes [5-6]Br, to be formed in 52-53 % yields (Scheme 6). Despite
lower efficiency, the transmetallation provides an alternative route to the preparation of N-
phosphonio-NHC metal complexes, and could be a valuable method for coordinating metallic
fragments bearing base sensitive co-ligands.
Pre-coordination of the carbenic center was expected to favor the anchorage of the
proximal phosphonium ylidic position. Treatment of NHC Pd(allyl)Cl complexes [6-8](OTf)
with one equivalent of potassium tert-butoxyde (tBuOK) in THF led to the targeted C,C-
chelating NHC-phosphonium ylide Pd(II) complexes [11-13](OTf), both isolated as a mixture
of two diastereoisomers ([11a,b](OTf): 75% (65/35); [12a,b](OTf): 69% (55/45);
2
4
31
[
13a,b](OTf): 80% (70/30)) (Scheme 7). The P NMR spectra displayed low-field
resonances, shifted of about 10 ppm relative to phosphonium precursors, suggesting the
formation of an ylide-metal bond ([11a,b](OTf):
ppm; [12a,b](OTf):
δ
P
+33.7; 34.5 ppm vs [6](OTf):
δ
P
+23.8
δ
P
+31.0; 32.1 ppm vs [7a,b](OTf):
δ
P
+23.8; 23.9 ppm; [13a,b](OTf):
1
1,12
δ
P
+33.9; 34.0 ppm vs [8](OTf);
δ
P
+24.2 ppm).
The existence of the [N
2
C−Pd−CH(R)–
+
13
P ] sequence was confirmed with the concomitant presence of high- and low-field C NMR
doublets for ylidic and carbenic carbon atoms respectively, as illustrated for complex
1
1
[
13a,b](OTf) (
δ
C
C
2.4 ppm (d, JCP = 32.2 Hz) and 2.5 ppm (d, JCP = 31.2 Hz); δ 203.9 ppm,
3
3
(
d, JCP = 2.0 Hz) and
δ
C
205.0 ppm, (d, JCP = 3.0 Hz)). Additional evidence was provided by
1
H NMR spectroscopy, with the presence of a ABX type system (ddd) for the ylidic CH atoms
in the +1.5-2.5 ppm zone. Noteworthy, NHC-phosphonium ylide Pd(II) complexes [11-
3](OTf) appear to be stable to hydrolysis and oxidation, both in the solid state and in
solution.
1
1
1

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Scheme 7. Access to the C,C-chelating NHC-phosphonium ylide Pd(II) complexes [11-
13](OTf) from their N-phosphonio-substituted NHC Pd(II) precursors [6-8](OTf).
The structure of complex [11a,b](OTf) was definitively established by X-ray diffraction
16
3 2
analysis of colorless single crystals deposited from CH CN/Et O (Figure 5). The Pd(II) atom
adopts a classical square planar geometry where the NHC and the phosphonium ylide ends act
in a cis-chelating manner with a C−Pd−C bite angle of 91.9(2)°. The C−Pd bond distances
(C1−Pd1 = 2.047(4); C6−Pd1 = 2.168(4) Å) fall within the range of those reported in related
11
2
3
Pd(II) complexes, with the Csp −Pd bond being significantly shorter than the Csp −Pd one.
The six-membered palladacycle adopts a quasi-half-chair conformation with the tetrahedral
phosphonium located in pseudo-equatorial position. The coordination of the stereogenic ylidic
carbon atom and the slow flip of the π-allyl co-ligand account for the existence of two
diastereoisomers in solution.
Figure 5. Perspective view of the cationic part of NHC-phosphonium ylide Pd(allyl) complex
[
11a,b](OTf), with thermal ellipsoids drawn at the 30 % probability level. Selected bond
lengths [Å] and angles [°]: [11a,b](OTf): C1−N1 = 1.366(5); C1−N2 = 1.354(4); C1−Pd1 =
.047(4); C6−Pd1 = 2.168(4); C7−Pd1 = 2.192(4); C9−Pd1 = 2.179(4); P1−C6 = 1.782(4);
N1−C1−N2 = 103.4(3); N1−C1−Pd1 = 132.5(3); N2−C1−Pd1 = 124.1(3); C1−Pd1−C6 =
1.9(2); P1−C6−Pd1 = 116.1(2); C5−C6−Pd1 = 115.9(3).
2
9
1
2

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Conclusion
A convenient one-step synthesis of N-phosphonio-substituted imidazolium salts [1-3]X
2
(X
=
Br, OTf) was developed with regard to the nature of the N-heterocycle and the alkyl bridge.
By taking advantage of the difference in acidity between the two cationic moieties, π-allyl
Pd(II) complexes of either monodentate NHC- [6-8](OTf) or chelating NHC-phosphonium
ylide ligands [11-13](OTf) based on a propyl bridge were selectively prepared. The method,
which was shown to tolerate different N-heterocycles, unsaturated or saturated, allowed the
first access of a representative of the NHC-phosphonium ylide family exhibiting a strongly
donating imidazolidin-2-ylidene ligand. NHC metal complexes ([5]Br: M = Rh(cod)Br; [6]Br:
M = Pd(allyl)Br) bearing a pendant phosphonium moiety could also be obtained through
transmetalation, involving as stable intermediate, the tetranuclear complex 9 of general
+
2-
2 4 6
formula [(NHC~P ) (Ag Br ) ]. The arrangement observed in the solid state, where two
positively charged NHCs are maintained by a bridging oligomeric dianion, results from the
minimization of repulsive effects of steric and electrostatic nature, promoting 9 as an
unprecedented doubly zwitterionic NHC Ag(I) complex. The growing diversity of N-
phosphonio-derived imidazolium salts, which are now readily available on a multi-gram scale,
should favor future developments, especially in the field of homogeneous catalysis. The
activation of non-reactive chemical bonds constitutes a possible prospect for electron-rich
NHC-phosphonium ylide ligands. The stabilization of electropositive and high-valent metal
centers which are largely involved in catalytic processes could also benefit from the advent of
these ligands.
Experimental Section
General Remarks. All manipulations were performed under an inert atmosphere of dry
nitrogen by using standard vacuum line and Schlenk tube techniques. Dry and oxygen-free
organic solvents (THF, Et
2
2 2
O, CH Cl , toluene, pentane) were obtained using a LabSolv
(Innovative Technology) solvent purification system. Acetonitrile was dried and distilled over
1
3
2
CaH . 1-(2, 4, 6-trimethylphenyl)-imidazole 1 and 4, 5-dihydro-1-(2, 4, 6-trimethylphenyl)-
14
imidazole 3 were prepared according to previously described procedures. All other reagents
were used as commercially available. Chromatographic purification was carried out on silica
1
31
13
gel (SiO
Avance III HD 400, and Avance 500 spectrometers. NMR chemical shifts
positive values to high frequency relative to the tetramethylsilane reference for H and C
2
, 63−200
ꢀ
m). H, P, and C NMR spectra were obtained on Bruker Avance 400,
δ
are in ppm, with
1
13
3
1
and to H
3 4
PO for P. If necessary, additional information on the carbon signal attribution was
1
3
1
31
13
1
13
obtained using C{ H, P}, J-modulated spin−echo (JMOD) C{1H}, H− C HMQC,
1
3

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and/or HMBC experiments. Mass spectra (ESI mode) were obtained using a Xevo G2 QTof
Waters) spectrometer and were performed by the mass spectrometry service of the “Institut
(
de Chimie de Toulouse”. Elemental analyses were carried out by the elemental analysis
service of the LCC (Toulouse, France) using a PerkinElmer 2400 series II analyzer.
1
-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazolium bromide [1]Br
-(2,4,6-trimethylphenyl)-imidazole 1 (1.00 g, 5.37 mmol), and (3-bromo-propyl)-
Cl (30
mL) for 15 hours. After evaporation of the solvent under vacuum, the crude residue was
washed with Et O (3 x 20 mL) affording [1]Br as a white powder (1.93 g, 84%).
Recrystallization from CH
2
1
6 5
triphenylphosphonium bromide (1.66 g, 3.58 mmol) were heated at 130 °C in C H
2
2
3
CN/Et
94 °C). P{ H} NMR (CD
s, 1H, N
CHMes), 4.72 (t, JHH = 6.9 Hz, 2H, NCH
2
O at room temperature gave colorless crystals (Mp = 292-
3
1
1
1
2
3
CN, 25 °C):
δ
= +24.16 (s); H NMR (CD
3
CN, 25 °C):
δ
= 9.94
(
2
CH), 7.68-7.92 (m, 16H, CHIm, CHPh), 7.43 (t, JHH = 1.8 Hz, 1H, CHIm), 7.10 (s, 2H,
), 3.76 (m, 2H, PCH ), 2.33 (s, 3H, CH3Mes), 2.32 (m,
), 2.06 (s, 6H, CH3Mes); C{ H} NMR (CD CN, 25 °C): 142.96 (s, CMes), 139.63
CH), 136.98 (d, JCP = 3.0 Hz, CHPh), 136.47 (s, CMes), 135.72 (d, JCP = 10.3 Hz, CHPh),
32.76 (s, CMes), 132.10 (d, JCP = 12.7 Hz, CHPh), 131.28 (s, CHMes), 125.60 (s, CHIm), 124.98
2
2
13
1
2H, CH
2
3
δ =
(s, N
2
1
(
s, CHIm), 119.72 (d, JCP = 87.0 Hz, CPh), 50.73 (d, JCP = 20.6 Hz, NCH
2
2
), 24.87 (s, CH ),
+
21.92 (s, CH3Mes), 21.09 (d, JCP = 54.5 Hz, PCH
2
), 18.55 (s, CH3Mes); MS (ES ): m/z: 569.0
+
[
M − Br] ; Elemental analysis for C33
H
35Br
2
N
2
P: calcd, C 60.94, H 5.42, N 4.31; found, C
60.72, H 5.12, N 4.26.
1
-mesityl-3-(2-(triphenylphosphonio)eth-1-yl)-imidazolium bromide [1’]Br
-(2, 4, 6-trimethylphenyl)-imidazole 1 (1.00 g, 5.37 mmol) and (2-bromo-ethyl)-
Cl (30
mL) for 15 hours. After evaporation of the solvent under vacuum, the crude residue was
2
1
6 5
triphenylphosphonium bromide (1.61 g, 3.58 mmol) were heated at 130 °C in C H
washed with Et
1’]Br as a white powder (1.92 g, 84%). P{ H} NMR (CD
NMR (CD CN, 25 °C): = 10.22 (brs, 1H, N
.06 (m, 6H, CHPh), 7.91-7.95 (m, 3H, CHPh), 7.75-7.80 (m, 6H, CHPh), 7.45 (t, JHH = 1.8 Hz,
H, CHIm), 7.11 (s, 2H, CHMes), 4.75-4.91 (m, 4H, CH ), 2.36 (s, 3H, CH3Mes), 2.10 (s, 6H,
= 141.20 (s, CMes), 138.49 (s, N CH), 135.47 (d,
CP = 3.0 Hz, CHPh), 134.79 (s, CMes), 134.25 (d, JCP = 11.1 Hz, CHPh), 131.00 (s, CMes),
2
O (3 x 20 mL). Recrystallization from CH
3
CN at room temperature gave
3
1
1
1
[
2
3
CN, 25 °C):
δ
= +20.99 (s); H
3
δ
2
CH), 8.33 (t, JHH = 1.8 Hz, 1H, CHIm), 8.01-
8
1
2
1
3
1
CH3Mes). C{ H} NMR (CD
3
CN, 25 °C):
δ
2
J
1
1
30.45 (d, JCP = 13.1 Hz, CHPh), 129.44 (s, CHMes), 123.91 (s, CHIm), 123.29 (s, CHIm),
17.13 (d, JCP = 87.5 Hz, CPh), 43.60 (d, JCP = 4.0 Hz, NCH ), 23.22 (d, JCP = 52.3 Hz,
2
1
4

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+
+
PCH
2
), 20.15 (s, CH3Mes), 16.91 (s, CH3Mes); MS (ES ): m/z: 555.2 [M − Br] ; Elemental
analysis for C32
H
2 2 2
33Br N P.H O: calcd, C 58.73, H 5.39, N 4.28; found, C 57.91, H 5.20, N
4.28.
1-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazolium trifluoromethanesulfonate
[
1](OTf)
2
[
1]Br
2
(0.25 g, 0.38 mmol) and sodium trifluoromethanesulfonate (0.17 g, 0.98 mmol) were
dissolved in CH
After evaporation of the solvent under vacuum, the crude residue was washed with water (20
mL), and the organic layer was extracted with CH Cl (2 x 20 mL), dried over Na SO
affording [1](OTf) as a white powder (0.25 g, 84%). Recrystallization from CH CN/Et O at
, 25 °C):
3
CN (20 mL) and the solution was stirred at room temperature for 15 hours.
2
2
2
4
,
2
3
2
3
1
1
room temperature gave colorless crystals (Mp = 195-197°C). P{ H} NMR (CDCl
3
1
δ
= +23.80 (s); H NMR (CDCl
3
, 25 °C):
δ
= 9.16 (s, 1H, N
2
CH), 8.09 (t, JHH = 1.6 Hz, 1H,
CHIm), 7.62-7.82 (m, 15H, CHPh), 7.13 (t, JHH = 1.6 Hz, 1H, CHIm), 6.94 (s, 2H, CHMes), 4.81
(
m, 2H, NCH
2
1
), 3.45 (m, 2H, PCH
2
), 2.35 (m, 2H, CH
2
), 2.28 (s, 3H, CH3Mes), 1.94 (s, 6H,
CH), 135.34 (d,
13
CH3Mes); C{ H} NMR (CDCl
3
, 25 °C):
δ
= 141.28 (s, CMes), 136.91 (s, N
2
J
CP = 3.0 Hz, CHPh), 133.99 (s, CMes), 133.63 (d, JCP = 10.3 Hz, CHPh), 130.63 (d, JCP = 12.7
Hz, CHPh), 130.51 (s, CMes), 129.83 (s, CHMes), 124.20 (s, CHIm), 123.72 (s, CHIm), 120.58 (q,
J
CF = 320.2 Hz, CF
3
), 117.28 (d, JCP = 86.9 Hz, CPh), 49.22 (d, JCP = 23.9 Hz, NCH
2
), 24.68
+
(
s, CH
2
), 21.03 (s, CH3Mes), 19.72 (d, JCP = 55.5 Hz, PCH
2
), 17.23 (s, CH3Mes); MS (ES ): m/z:
+
6
39.3 [M − CF
3
SO
3
] . Elemental analysis for C35
H
35
F
6
N
2
O
6
PS
2
: calcd, C 53.30, H 4.47, N
3.35; found, C 53.39, H 4.24, N 3.42.
1
-methyl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazolium bromide [2]Br
-methyl-imidazole 2 (0.27 g, 3.23 mmol), and (3-bromo-propyl)-triphenylphosphonium
Cl (20 mL) for 15 hours. After
evaporation of the solvent under vacuum, the crude residue was washed with Et O (3 x 20
mL) affording [2]Br as a white powder (1.14 g, 97%). Recrystallization from CH Cl /Et O at
CN, 25 °C):
2
1
6 5
bromide (1.0 g, 2.15 mmol) were heated at 130 °C in C H
2
2
2
2
2
3
1
1
room temperature gave colorless crystals (Mp = 262-264 °C). P{ H} NMR (CD
3
1
δ
= +24.19 (s); H NMR (CD
3
CN, 25 °C):
δ
= 9.51 (s, 1H, N
2
CH), 7.83-7.91 (m, 9H, CHPh),
7.72-7.76 (m, 6H, CHPh), 7.66 (brs, 1H, CHIm), 7.38 (brs 1H, CHIm), 4.62 (t, JHH = 8.0 Hz, 2H,
1
3
1
NCH
2
), 3.89 (s, 3H, NCH
= 137.18 (s, N
CHPh), 130.29 (d, JCP = 12.1 Hz, CHPh), 123.58 (s, CHIm), 122.44 (s, CHIm), 117.94 (d, JCP
7.5 Hz, CPh), 48.50 (d, JCP = 20.1 Hz, NCH ), 35.99 (s, NCH ), 23.30 (s, CH ), 19.12 (d, JCP
3
), 3.75 (m, 2H, PCH
2 2 3
), 2.22 (m, 2H, CH ); C{ H} NMR (CD CN,
25 °C):
δ
2
CH), 135.15 (d, JCP = 3.0 Hz, CHPh), 133.93 (d, JCP = 10.1 Hz,
=
8
2
3
2
1
5

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+
+
=
54.3 Hz, PCH
2
); MS (ES ): m/z: 465.3 [M − Br] . Elemental analysis for C25
H
27Br
2
N
2
P:
calcd, C, 54.97 H, 4.98 N 5.13; found, C, 54.37 H, 4.66 N, 5.01.
1-methyl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazolium trifluoromethanesulfonate
[
2](OTf)
2
[
2]Br
2
(1.05 g, 1.92 mmol) and sodium trifluoromethanesulfonate (0.83 g, 4.81 mmol) were
dissolved in CH
After evaporation of the solvent under vacuum, the crude residue was washed with water (20
mL), and the organic layer was extracted with CH Cl (2 x 20 mL), dried over Na SO
affording [2](OTf) as a white powder (1.21 g, 92%). Recrystallization from CH CN/Et O at
CN, 25 °C):
3
CN (20 mL) and the solution was stirred at room temperature for 15 hours.
2
2
2
4
,
2
3
2
3
1
1
room temperature gave colorless crystals (Mp = 116-118 °C). P{ H} NMR (CD
3
1
δ
7
2
= +23.72 (s); H NMR (CD
3
CN, 25 °C):
δ
= 8.69 (s, 1H, N
2
CH), 7.88-7.93 (m, 3H, CHPh),
.73-7.79 (m, 12H, CHPh), 7.45 (brs, 1H, CHIm), 7.40 (brs 1H, CHIm), 4.40 (t, JHH = 8.0 Hz,
13
1
H, NCH
CN, 25 °C):
Hz, CHPh), 130.38 (d, JCP = 13.1 Hz, CHPh), 124.00 (s, CHIm), 122.28 (s, CHIm), 121.07 (q, JCF
2
), 3.86 (s, 3H, NCH
3
), 3.34 (m, 2H, PCH
2 2
), 2.19 (m, 2H, CH ); C{ H} NMR
(CD
3
δ
= 136.64 (s, N
2
CH), 135.30 (d, JCP = 3.0 Hz, CHPh), 133.73 (d, JCP = 10.1
=
320.9 Hz, CF
3
2
), 117.68 (d, JCP = 86.5 Hz, CPh), 48.83 (d, JCP = 21.1 Hz, NCH ), 35.93 (s,
+
NCH
3
), 23.11 (d, JCP = 3.0 Hz, CH
2
), 18.91 (d, JCP = 55.3 Hz, PCH
PS
2
); MS (ES ): m/z: 535.4
+
[
M − CF
3
SO
3
] . Elemental analysis for C27
H
27
6
F N
2
O
6
2
: calcd, C, 47.37 H, 3.98 N 4.09;
found, C, 47.59 H, 3.75 N, 4.13.
1-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-4,5-dihydro-imidazolium
bromide
[3]Br
2
4, 5-dihydro-1-(2, 4, 6-trimethylphenyl)-imidazole 3 (1.42 g, 7.55 mmol) and (3-
bromopropyl)-triphenylphosphonium bromide (2.93 g, 6.29 mmol) were heated at 70 °C in
CH CN (20 mL) for 18 hours. After evaporation of the solvent under vacuum, the crude
residue was washed with Et O (3 x 20 mL) affording [3]Br as a white powder (3.04 g, 74%).
Recrystallization from CH CN/Et O at room temperature gave colorless crystals (Mp = 245-
3
2
2
3
2
3
1
1
1
2
47 °C). P{ H} NMR (CD
s, 1H, N
CH2Im), 3.95-4.10 (m, 4H, PCH2, CH2Im), 2.29 (s, 3H, CH3Mes), 2.00-2.15 (m, 2H, CH
3
CN, 25 °C):
3
δ = +24.80 (s); H NMR (CD CN, 25 °C): δ = 9.49
(
2
CH), 7.65-7.97 (m, 15H, CHPh), 7.01 (s, 2H, CHMes), 4.11-4.32 (m, 4H, NCH2,
), 1.96
CH), 141.27 (s, CMes),
36.99 (s, CMes), 136.20 (d, JCP = 2.9 Hz, CHPh), 135.23 (d, JCP = 10.3 Hz, CHPh), 132.23 (s,
2
13
1
(
3 2
s, 6H, CH3Mes); C{ H} NMR (CD CN, 25 °C): δ = 160.72 (s, N
1
C
Mes), 131.35 (d, JCP = 12.7 Hz, CHPh), 130.78 (s, CHMes), 119.44 (d, JCP = 86.8 Hz, CPh),
), 21.24 (s, CH3Mes), 20.98
52.19 (s, CH2Im), 49.87 (s, CH2Im), 48.41 (d, JCP = 18.9 Hz, NCH
2
1
6

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+
+
(
s, CH
2
), 20.44 (d, JCP = 53.0 Hz, PCH
2
), 18.55 (s, CH3Mes); MS (ES ): m/z: 571.0 [M − Br] ;
Elemental analysis for C33
N 4.26.
2 2
H37Br N P: calcd, C 60.75, H 5.72, N 4.29; found, C 60.42, H 6.02,
1
-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-4,5-dihydro-imidazolium
methanesulfonate [3](OTf)
3]Br (0.85 g, 1.30 mmol) and sodium trifluoromethanesulfonate (0.56 g, 3.26 mmol) were
dissolved in CH CN (20 mL) and the solution was stirred at room temperature for 15 hours.
After evaporation of the solvent under vacuum, the crude residue was washed with water (20
mL), and the organic layer was extracted with CH Cl (2 x 20 mL), dried over Na SO
affording [3](OTf) as a white powder (1.0 g, 97%). Recrystallization from CH CN/Et O at
CN, 25 °C):
trifluoro-
2
[
2
3
2
2
2
4
,
2
3
2
3
1
1
room temperature gave colorless crystals (Mp = 82-84 °C). P{ H} NMR (CD
3
δ
1
=
+23.91 (s); H NMR (CD
3
CN, 25 °C):
δ
= 8.20 (brs, 1H, N
2
CH), 7.90-7.95 (m, 3H, CHPh),
7
.75-7.82 (m, 12H, CHPh), 7.05 (s, 2H, CHMes), 4.06-4.23 (m, 4H, CH2Im), 3.79 (t, JHH = 8.0
Hz, 2H, NCH ), 3.35 (m, 2H, PCH ), 2.32 (s, 3H, CH3Mes), 2.28 (s, 6H, CH3Mes), 2.09 (m, 2H,
); C{ H} NMR (CD CN, 25 °C): = 158.84 (s, N CH), 140.34 (s, CMes), 135.75 (s,
Mes), 135.32 (d, JCP = 2.0 Hz, CHPh), 133.76 (d, JCP = 11.1 Hz, CHPh), 130.75 (s, CMes),
30.39 (d, JCP = 12.1 Hz, CHPh), 129.61 (s, CHMes), 121.06 (q, JCF = 319.9 Hz, CF ), 117.80
d, JCP = 88.5 Hz, CPh), 50.88 (s, CH2Im), 48.75 (s, CH2Im), 47.93 (d, JCP = 21.1 Hz, NCH ),
), 16.80 (s,
PS
2
2
1
3
1
CH
2
3
δ
2
C
1
3
(
2
2
0.19 (d, JCP = 3.0 Hz, CH
2
), 20.05 (s, CH3Mes), 19.20 (d, JCP = 54.3 Hz, PCH
2
+
+
CH3Mes); MS (ES ): m/z: 641.2 [M − CF
3
SO
3
] ; Elemental analysis for C35
H
37
F
6
N
2
O
6
2
:
calcd, C 53.16, H 4.72, N 3.54; found, C 52.76, H 4.66, N 3.64.
Vinyl triphenylphosphonium bromide [4]Br
[
1’]Br
CH CN (2 mL). The suspension was stirred at room temperature for 6 hours. After filtration
over celite, the solvent was evaporated under vacuum. Washing with Et O (2 x 10 mL)
afforded [4]Br as a white solid (0.02 g, 91%). The structure of [4]Br was confirmed
2 2 3
(0.06 g, 0.09 mmol), and anhydrous K CO (0.01 g, 0.10 mmol) were dissolved in
3
2
18
unambiguously by comparison of the NMR data with those from the literature.
1
7

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4
1
1
1
-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazol-2-yliden-bromo(
η
-cycloocta-
,5-diene)rhodium(I) bromide [5]Br
st
method: Dication [1]Br
2
(0.10 g, 0.15 mmol), [RhCl(cod)
2
] (0.04 g, 0.08 mmol), and
anhydrous K
2
CO (0.02 g, 0.17 mmol) were dissolved in CH
3
3
CN (10 mL). The suspension
was stirred at room temperature for 15 hours. After filtration over celite and evaporation of
the solvent under vacuum, [5]Br was obtained as a yellow solid (0.12 g, 93%).
nd
2
method: Silver complex 9 (0.15 g, 0.08 mmol) and [RhCl(cod)
Cl (10 mL), and the solution was stirred at room temperature for 15 hours.
After filtration over celite, the solvent was evaporated under vacuum. After washing with
Et O (3 x 10 mL), [5]Br was obtained as a yellow solid (0.06 g, 87%). Recrystallization from
CH
2
] (0.02 g, 0.04 mmol) were
dissolved in CH
2
2
2
31
1
3
CN/Et
2
O at room temperature gave yellow crystals (Mp = 233-235 °C). P{ H} NMR
1
(
CD
3
CN, 25 °C):
δ
= +24.02 (s); H NMR (CD
3
CN, 25 °C):
δ
= 7.90 (brs, 1H, CHMes), 7.83-
7
.88 (m, 8H, CHPh), 7.67-7.74 (m, 7H, CHPh), 7.05 (brs, 1H, CHIm), 6.97 (brs, 1H, CHIm),
.90 (d, JHH = 3.0 Hz, 1H, CHMes), 5.14 (m, 1H, NCH ), 4.95 (m, 1H, NCH ), 4.80 (brs, 1H,
), 3.60 (m, 1H, PCH ), 3.30 (brs, 1H, CHcod),
.10 (brs, 1H, CHcod), 2.33 (s, 3H, CH3Mes), 2.28 (s, 3H, CH3Mes), 1.78 (s, 3H, CH3Mes), 1.40-
6
2
2
CHcod), 4.57 (brs, 1H, CHcod), 3.93 (m, 1H, PCH
2
2
3
2
1
13
.55 (m, 10H, CH
39.71 (s, CMes), 137.27 (s, CMes), 137.07 (s, CMes), 136.09 (d, JCP = 2.9 Hz, CHPh), 135.90 (s,
Mes), 134.91 (d, JCP = 10.2 Hz, CHPh), 131.30 (d, JCP = 12.6 Hz, CHPh), 130.13 (s, CHMes),
29.25 (s, CHMes), 125.06 (s, CHIm), 123.05 (s, CHIm), 119.31 (d, JCP = 86.5 Hz, CPh), 97.16
d, JCRh = 6.8 Hz, CHcod), 96.22 (d, JCRh = 6.2 Hz, CHcod), 70.39 (d, JCRh = 14.1 Hz, CHcod),
9.46 (d, JCRh = 14.2 Hz, CHcod), 51.60 (d, JCP = 20.5 Hz, NCH ), 34.32 (s, CH2 cod), 32.15 (s,
2 3 2
, CH2cod); C NMR (CD CN, 25 °C): δ = 182.12 (d, JCRh = 50.9 Hz, N C),
C
1
(
6
2
CH2 cod), 29.88 (s, CH2 cod), 28.99 (s, CH2 cod), 24.72 (d, JCP = 2.8 Hz, CH
2
), 21.25 (s, CH3Mes),
+
+
19.88 (d, JCP = 50.5 Hz, PCH
2
), 18.23 (s, CH3Mes); MS (ES ): m/z 779.0 [M − Br] ; Elemental
analysis calculated for C41
N 3.03.
H46Br
2
N
2
PRh: C 57.23, H 5.39, N 3.26; obtained: C 57.18, H 5.93,
3
1-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazol-2-yliden-bromo(
η
-2-propen-1-
yl)palladium(II) bromide [6]Br
st
1
method: Dication [1]Br
2
(0.10 g, 0.15 mmol), [Pd(allyl)Cl]
2
(0.03 g, 0.09 mmol), and
anhydrous K
2
CO (0.02 g, 0.17 mmol) were dissolved in CH
3
3
CN (10 mL). The suspension
was stirred at room temperature for 15 hours. After filtration over celite and evaporation of
the solvent under vacuum, [6]Br was obtained as a white solid (0.12 g, 95%).
nd
2
method: Silver complex 9 (0.09 g, 0.05 mmol) and [Pd(allyl)Cl]
2
(0.009 g, 0.03 mmol)
were dissolved in CH
2
Cl (10 mL), and the solution was stirred at room temperature for 15
2
1
8

Page 19 of 28
Dalton Transactions
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DOI: 10.1039/C7DT02759A
hours. After filtration over celite, the solvent was evaporated under vacuum, and [6]Br was
31
1
obtained as a white crystalline solid (0.07 g, 88%); (Mp = 118-120 °C). P{ H} NMR
1
(
CD
3
CN, 25 °C):
δ
= +23.89 (s); H NMR (CD
3
CN, 25 °C):
δ
= 7.71-7.90 (m, 15H, CHPh),
7
6
1
.53 (d, JHH = 1.8 Hz, 1H, CHIm), 7.12 (d, JHH = 1.8 Hz, 1H, CHIm), 7.01 (brs, 1H, CHMes),
.99 (brs, 1H, CHMes), 4.97 (m, 1H, CHallyl), 4.55-4.62 (m, 2H, NCH ), 3.87 (d, JHH = 7.3 Hz,
H, CH2allyl), 3.51-3.66 (m, 2H, PCH ), 3.27 (brs, 1H, CH2allyl), 2.80 (d, JHH = 13.4 Hz, 1H,
2
2
CH2allyl), 2.31 (s, 3H, CH3Mes), 2.26-2.34 (m, 3H, CH2, CH2allyl), 2.11 (s, 3H, CH3Mes), 2.01 (s,
1
3
1
3
H, CH3Mes); C{ H} NMR (CD
s, CMes), 135.56 (s, CMes), 135.43 (s, CMes), 135.13 (d, JCP = 2.0 Hz, CHPh), 133.80 (d, JCP
0.1 Hz, CHPh), 130.30 (d, JCP = 13.1 Hz, CHPh), 128.76 (s, CHMes), 128.64 (s, CHMes), 123.56
s, CHIm), 121.96 (s, CHIm), 118.16 (d, JCP = 86.5 Hz, CPh), 114.58 (s, CHallyl), 70.62 (s,
3 2
CN, 25 °C): δ = 180.90 (s, N C), 138.87 (s, CMes), 136.22
(
=
1
(
CH2allyl), 50.00 (d, JCP = 19.1 Hz, NCH
2
), 23.75 (d, JCP = 3.0 Hz, CH
2
), 20.15 (s, CH3Mes),
+
19.50 (d, JCP = 53.3 Hz, PCH
2
), 17.66 (s, CH3Mes), 17.44 (s, CH3Mes); MS (ES ): m/z 717.1 [M
+
−
Br] ; Elemental analysis calculated for C36
H
39Br
2
N
2
PPd.0.8CH
2
Cl
2
: C 51.11, H 4.73,
N 3.24; obtained: C 51.35, H 4.79, N 3.26.
3
1
-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazol-2-yliden-chloro(
yl)palladium(II) trifluoromethanesulfonate [6](OTf)
A mixture of [Pd(allyl)Cl] (0.07 g, 0.19 mmol), dication [1](OTf)
anhydrous K CO (0.16 g, 1.13 mmol), was dissolved in CH CN (20 mL) and stirred at room
η
-2-propen-1-
2
2
(0.30 g, 0.38 mmol), and
2
3
3
temperature for 12 hours. After filtration over celite, the solvent was removed under vacuum.
The remaining solid residue was purified by chromatography on silica gel (AcOEt) affording
[
6](OTf) as a yellow crystalline solid (0.27 g, 87%). Recrystallization from CH
2
Cl
2 2
/Et O at
31
1
room temperature gave yellow crystals (Mp = 112-114 °C). P{ H} NMR (CD
3
CN, 25 °C): δ
1
=
+23.80 (s); H NMR (CD
3
CN, 25 °C):
δ
= 7.88-7.92 (m, 3H, CHPh), 7.71-7.80 (m, 12H,
CHPh), 7.37 (d, JHH = 1.6 Hz, 1H, CHIm), 7.14 (d, JHH = 1.6 Hz, 1H, CHIm), 7.02 (brs, 1H,
CHMes), 7.00 (brs, 1H, CHMes), 5.00 (m, 1H, CHallyl), 4.52 (m, 2H, NCH ), 3.90 (brs, 1H,
CH2allyl), 3.20-3.55 (m, 3H, PCH2, CH2allyl), 2.83 (d, JHH = 13.5 Hz, 1H, CH2allyl), 2.33 (s, 3H,
2
13
1
CH3Mes), 2.20-2.35 (m, 3H, CH2, CH2allyl), 2.11 (s, 3H, CH3Mes), 2.02 (s, 3H, CH3Mes); C{ H}
NMR (CDCl , 25 °C): = 180.10 (s, N C), 138.67 (s, CMes), 136.31 (s, CMes), 135.68 (s,
Mes), 135.10 (s, CMes), 134.99 (d, JCP = 3.0 Hz, CHPh), 133.85 (d, JCP = 10.1 Hz, CHPh),
30.50 (d, JCP = 13.1 Hz, CHPh), 129.02 (s, CHMes), 128.73 (s, CHMes), 122.83 (s, CHIm),
20.55 (q, JCF = 320.0 Hz, CF ), 118.07 (d, JCP = 86.5 Hz, CPh), 114.79 (s, CHallyl), 72.66 (s,
), 49.17 (s, CH2allyl), 24.51 (d, JCP = 3.0 Hz, CH ),
1.06 (s, CH3Mes), 20.31 (d, JCP = 53.3 Hz, PCH ), 18.46 (s, CH3Mes), 18.02 (s, CH3Mes); MS
3
δ
2
C
1
1
3
CH2allyl), 50.39 (d, JCP = 21.1 Hz, NCH
2
2
2
2
1
9

Dalton Transactions
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DOI: 10.1039/C7DT02759A
+
+
(
ES ): m/z: 671.2 [M − CF
3
SO
3
] . Elemental analysis for C37
H39ClF
3
N
2
O
3
2
PPdS.4H O: calcd,
C, 49.73 H, 5.30 N 3.13; found, C, 49.76 H, 4.15 N 3.23.
3
1
-methyl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazol-2-yliden-chloro(
yl)palladium(II) trifluoromethanesulfonate [7a,b](OTf)
A mixture of [Pd(allyl)Cl] (0.13 g, 0.37 mmol), dication [2](OTf)
anhydrous K CO (0.30 g, 2.19 mmol), was dissolved in CH CN (20 mL) and stirred at room
η
-2-propen-1-
2
2
(0.50 g, 0.73 mmol), and
2
3
3
temperature for 15 hours. After filtration over celite, the solvent was removed under vacuum.
The remaining solid residue was purified by chromatography on silica gel (AcOEt) affording
a yellow powder as a mixture (
≈
55/45) of two diastereoisomers [7a,b](OTf) (0.47 g, 91%).
3
1
1
1
(
Mp = 78-80 °C). P{ H} NMR (CD
CD CN, 25 °C):
3
CN, 25 °C):
δ
= +23.78 (s), +23.87 (s); H NMR
(
3
δ
= 7.42-7.47 (m, 6H, CHPh), 7.24-7.32 (m, 24H, CHPh), 6.74 (brs, 2H,
CHIm), 6.72 (brs, 1H, CHIm), 6.70 (brs, 1H, CHIm), 5.39 (m, 1H, CHallyl), 5.25 (m, 1H, CHallyl),
4
.30 (t, JHH = 6.3 Hz, 2H, NCH
2
), 4.21 (m, 2H, NCH
2
), 4.01-4.08 (m, 2H, CH2allyl), 3.78 (s,
), 3.11-3.48 (m, 5H, PCH2,
3
H, NCH ), 3.68 (d, JHH = 7.2 Hz, 1H, CH2allyl), 3.59 (s, 3H, NCH
3
3
CH2allyl), 2.54 (d, JHH = 13.3 Hz, 1H, CH2allyl), 2.50 (brs, 1H, CH2allyl), 2.10-2.25 (m, 6H, CH2,
1
3
1
3 2
CH2allyl); C{ H} NMR (CD CN, 25 °C): δ = 175.87 (brs, N C), 134.83 (d, JCP = 3.0 Hz,
CHPh), 134.75 (d, JCP = 3.0 Hz, CHPh), 133.26 (d, JCP = 10.1 Hz, CHPh), 133.24 (d, JCP = 10.1
Hz, CHPh), 129.91 (d, JCP = 12.1 Hz, CHPh), 129.87 (d, JCP = 12.1 Hz, CHPh), 123.57 (s, CHIm),
1
23.02 (s, CHIm), 121.30 (s, CHIm), 121.17 (s, CHIm), 120.61 (q, JCF = 319.9 Hz, CF
s, CHallyl), 117.52 (d, JCP = 86.5 Hz, CPh), 117.31 (d, JCP = 87.5 Hz, CPh), 72.20 (brs, CH2allyl),
9.47 (d, JCP = 19.1 Hz, NCH ), 49.44 (d, JCP = 19.1 Hz, NCH ), 48.49 (brs, CH2allyl), 37.44
s, NCH ), 37.09 (s, NCH ), 23.63 (d, JCP = 3.0 Hz, CH
d, JCP = 54.3 Hz, PCH ), 18.51 (d, JCP = 54.3 Hz, PCH
3
), 118.98
(
4
2
2
(
(
3
3
2
), 23.21 (d, JCP = 3.0 Hz, CH
2
), 18.65
+
+
2
2
); MS (ES ): m/z: 681.1 [M − Cl] .
Elemental analysis for C29
H, 4.09 N 3.85.
3 2 3
H31ClF N O PPdS: calcd, C, 48.55 H, 4.36 N 3.90; found, C, 47.60
1-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-4,5-dihydro-imidazol-2-yliden-chloro
3
η
(
-2-propen-1-yl)palladium(II) trifluoromethanesulfonate [8](OTf)
A mixture of [Pd(allyl)Cl] (0.26 g, 0.71 mmol), dication [3](OTf) (1.12 g, 1.42 mmol), and
anhydrous K CO (0.59 g, 4.26 mmol), was dissolved in CH CN (20 mL) and stirred at room
2
2
2
3
3
temperature for 15 hours. After filtration over celite, the solvent was removed under vacuum.
The remaining solid residue was purified by chromatography on silica gel (AcOEt) affording
31
1
[
3
8](OTf) as a white powder (1.08 g, 93%); (Mp = 118-120 °C). P{ H} NMR (CD CN, 25
1
°C):
δ
= +24.25 (s); H NMR (CD
3
CN, 25 °C):
δ
= 7.73-7.93 (m, 15H, CHPh), 6.95 (s, 1H,
2
0

Page 21 of 28
Dalton Transactions
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DOI: 10.1039/C7DT02759A
2
CHMes), 6.93 (s, 1H, CHMes), 4.92 (m, 1H, CHallyl), 3.96 (m, 2H, NCH ), 3.80-3.87 (m, 3H,
CH2Im, CH2allyl), 3.67-3.70 (m, 2H, CH2Im), 3.48-3.56 (m, 3H, PCH
2
, CH2allyl), 2.74 (d, JHH =
13.6 Hz, 1H, CH2allyl), 2.34 (s, 3H, CH3Mes), 2.28 (s, 6H, CH3Mes), 2.00-2.11 (m, 3H, CH2,
1
3
1
CH2allyl); C{ H} NMR (CD
Mes), 136.50 (s, CMes), 136.20 (s, CMes), 135.16 (d, JCP = 2.0 Hz, CHPh), 133.76 (d, JCP = 10.1
Hz, CHPh), 130.29 (d, JCP = 13.1 Hz, CHPh), 128.99 (s, CHMes), 128.90 (s, CHMes), 121.10 (q,
CF = 320.9 Hz, CF ), 118.28 (d, JCP = 86.5 Hz, CPh), 114.75 (s, CHallyl), 70.79 (s, CH2allyl),
1.79 (s, CH ), 51.18 (s, CH ), 49.68 (d, JCP = 18.1 Hz, NCH ), 48.29 (s, CH2allyl), 20.45 (d,
CP = 4.0 Hz, CH ), 20.06 (s, CH3Mes), 19.56 (d, JCP = 53.3 Hz, PCH ), 17.86 (s, CH3Mes),
7.61 (s, CH3Mes); MS (ES ): m/z: 319.1 [(M – (CF + Cl))/2] . Elemental analysis for
PPdS.0.5CH Cl : calcd, C, 52.00 H, 4.89 N 3.23; found, C, 52.11 H, 4.80 N
3 2
CN, 25 °C): δ = 208.96 (s, N C), 137.98 (s, CMes), 136.57 (s,
C
J
3
5
2
2
2
J
2
2
+
+
1
3 3
SO
C
37
H
41ClF
3
N
2
O
3
2
2
3.17.
Bis[1-mesityl-3-(3-(triphenylphosphonio)prop-1-yl)-imidazol-2-yliden], [Ag
bis[1-mesityl-3-(3-(oxo-diphenylphosphino)prop-1-yl)-imidazol-2-yliden], [Ag
1]Br (0.50 g, 0.77 mmol) and Ag O (0.27 g, 1.11 mmol) were dissolved in CH Cl
in presence of molecular sieves (4 Å), and the suspension was stirred at room temperature for
0 hours. After filtration over celite, and evaporation of the solvent under vacuum, 9 was
obtained as a white solid (0.85 g, 60%). Recrystallization from CH Cl /Et O at room
4
Br
6
] 9, and
] 10
(20 mL)
2
Br
2
[
2
2
2
2
6
2
2
2
temperature gave colorless crystals of 9 (Mp = 143-145 °C). In the same conditions, but in the
absence of molecular sieves, 10 was obtained as a white solid (0.86 g, 90%). Recrystallization
from CH
Cl
2 2
/Et
2
O at room temperature gave colorless crystals of 10 (Mp = 165-167 °C).
3
1
1
1
9
: P{ H} NMR (CD
3
CN, 25 °C):
δ
= +23.72 (s); H NMR (CD
3
CN, 25 °C):
δ
= 7.65-7.91
(m, 30H, CHPh), 7.39 (d, JHH = 1.8 Hz, 2H, CHIm), 7.09 (d, JHH = 1.8 Hz, 2H, CHIm), 7.00 (s,
4
H, CHMes), 4.51 (t, JHH = 6.9 Hz, 4H, NCH
.15-2.26 (m, 4H, CH ), 1.90 (s, 12H, CH3Mes); C{ H} NMR (DMSO, 25 °C):
C), 138.88 (s, CMes), 135.95 (s, CMes), 135.37 (d, JCP = 2.9 Hz, CHPh), 134.72 (s, CMes),
33.82 (d, JCP = 10.2 Hz, CHPh), 130.64 (d, JCP = 12.6 Hz, CHPh), 129.23 (s, CHMes), 123.85
s, CHIm), 122.28 (s, CHIm), 118.39 (d, JCP = 86.3 Hz, CPh), 50.79 (d, JCP = 19.9 Hz, NCH ),
), 17.59 (s, CH3Mes); MS
Br : C
2
), 3.41-3.54 (m, 4H, PCH
2
), 2.33 (s, 6H, CH3Mes),
1
3
1
2
2
δ
= 181.07 (s,
N
2
1
(
2
2
4.35 (s, CH
2
), 20.88 (s, CH3Mes), 18.48 (d, JCP = 52.7 Hz, PCH
2
+
+
(ES ): m/z: 677.3 [(M
–
Ag
2
Br
4
)/2] ; Elemental analysis calculated for C66
H68Ag
4
6 4 2
N P
41.94, H 3.63, N 2.96. Obtained: C 41.40, H 3.69, N 3.29.
31
1
1
1
3 3
0: P{ H} NMR (CD CN, 25 °C): δ = +29.74 (s); H NMR (CD CN, 25 °C): δ = 7.46–7.75
(m, 20H, CHPPh), 7.35 (d, JHH = 1.5 Hz, 2H, CHIm), 7.10 (d, JHH = 1.5 Hz, 2H, CHIm), 6.98 (s,
2
1

Dalton Transactions
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DOI: 10.1039/C7DT02759A
4
H, CHMes), 4.26 (t, JHH = 6.7 Hz, 4H, NCH ),
2
), 2.33 (s, 6H, CH3Mes), 2.19–2.30 (m, 4H, CH
2
1
3
1
1
.97–2.11 (m, 4H, PCH ), 1.84 (s, 12H, CH3Mes); C{ H} NMR (CD CN, 25 °C): δ = 140.33
2
3
(
s, CMes), 136.78 (s, CMes), 135.97 (s, CMes), 134.51 (d, JCP = 97.8 Hz, CPh), 132.81 (d, JCP
.7 Hz, CHPh), 131.48 (d, JCP = 9.2 Hz, CHPh), 129.94 (d, JCP = 12.1 Hz, CHPh), 129.77 (s,
CHMes), 124.08 (s, CHIm), 122.70 (s, CHIm), 52.33 (d, JCP = 14.2 Hz, NCH ), 26.70 (d, JCP
2.2 Hz, PCH ), 24.85 (d, J = 3.3 Hz, CH ), 21.16 (s, CH3Mes), 17.76 (s, CH3Mes). MS (ES ):
=
2
2
=
+
7
2
CP
2
+
m/z: 965.2 [(M – AgBr
2 2 2 4 2 2
)] ; Elemental analysis calculated for C54H58Ag Br N O P : C 52.62,
H 4.74, N 4.55. Obtained: C 53.45, H 4.78, N 4.67.
3
prop-1,3-diyl)-imidazol-2-yliden-chloro( -2-
1-mesityl-3-(3-(triphenylphosphonio)
η
propen-1-yl)palladium(II) trifluoromethanesulfonate [11a,b](OTf)
A 1/1 mixture of tBuOK and complex [6](OTf) (0.23 g, 0.27 mmol) in presence of molecular
sieves (4 Å) was cooled to –78°C, and THF (10 mL) was added. The suspension was warmed
to room temperature and stirred for 2 hours. After evaporation of the solvent, the solid residue
was dissolved in CH Cl (10 mL) and filtered over celite. Purification by chromatography on
2
2
silica gel (CH Cl /AcOEt) gave a yellow solid as a mixture of two diastereoisomers
2
2
[
11a,b](OTf) (65/35) (0.16 g, 75%). Recrystallization from CH CN/Et O at −20°C gave
3 2
a
b
colorless crystals (Mp = 120-122 °C). NMR assignment: major isomer (65%); minor isomer
3
1
1
a
b
1
(
35%): P{ H} NMR (CD CN, 25 °C):
δ
= +33.71 (s), +34.54 (s); H NMR (CD CN, 25
3
3
a,b
a,b
a,b
°C):
δ
= 7.71-7.81 (m, 26H, CH ), 7.58-7.63 (m, 16H, CH ), 7.38 (m, 2.8H, CHIm),
Ph Ph
a,b
b
b
a
7
.12 (m, 2.8H, CH ), 7.10 (brs, 1H, CH ), 7.08 (brs, 1H, CH ), 7.06 (brs, 3.6H,
Im Mes Mes
a,b
b
a
CHMes), 4.40-4.50 (m, 2.8H, CHallyl), 4.29-4.34 (m, 1H, NCH ), 4.13-4.22 (m, 2.8H,
2
b
a,b
a
NCH ), 4.04-4.09 (m, 1H, NCH ), 2.70-2.74 (m, 2.8H, CH2allyl), 2.58 (ddd, J = 7.1, 10.3
2
2
HH
b
Hz, JHP = 12.9 Hz, 1.8H, PCH), 2.40 (ddd, J = 5.8, 11.0 Hz, JHP = 13.8 Hz, 1H, PCH),
HH
b
a
a
b
2
2
J
.37 (s, 3H, CH3 ), 2.34 (s, 5.4H, CH ), 2.11 (s, 5.4H, CH ), 2.09 (s, 3H, CH3Mes),
Mes 3Mes 3Mes
b
a
a,b
b
.01 (s, 3H, CH3 ), 1.96 (s, 5.4H, CH3Mes), 1.94-2.14 (m, 8.4H, CH CH
), 1.81 (d,
Mes
2,
2allyl
a
b
= 13.2 Hz, 1H, CH2allyl), 1.54 (d, J = 13.1 Hz, 1.8H, CH2allyl), 1.44 (d, J = 13.0 Hz,
HH
HH
HH
a
13
1
1
1
1
1
H, CH2allyl), 1.34 (d, J = 13.2 Hz, 1.8H, CH2allyl); C{ H} NMR (CD CN, 25 °C): δ =
H
H
3
a
b
b
a
76.79 (d, J = 2.5 Hz, N C), 175.58 (brs, N C), 139.18 (s, C ), 139.10 (s, CMes),
CP
2
2
Mes
b
a
a,b
a,b
a,b
37.35 (s, C ), 137.18 (s, CMes), 135.71 (s, CMes), 135.45 (s, CMes), 135.17 (s, CMes),
Mes
b
a
b
33.43 (d, J = 8.8 Hz, CH ), 133.40 (d, J = 7.5 Hz, CH ), 133.27 (d, J = 3.8 Hz,
CP
Ph
CP
Ph
CP
a
b
a
CH ), 133.15 (d, J = 2.5 Hz, CH ), 129.31 (d, J = 11.3 Hz, CH ), 129.26 (d, J
=
Ph
CP
Ph
CP
Ph
CP
b
a
b
a
1
1.3 Hz, CH ), 128.83 (s, CH ), 128.77 (s, CH ), 128.76 (s, CH ), 128.69 (s,
Ph Mes Mes Mes
a
b
b
CHMes), 124.72 (d, J = 83.0 Hz, C ), 124.66 (d, J = 83.0 Hz, C ), 122.43 (s, CH ),
CP
Ph
CP
Ph
Im
b
a
a
a,b
1
22.12 (s, CH ), 122.10 (s, CH ), 122.04 (s, CH ), 121.22 (q, JCF = 322.0 Hz, CF3),
Im Im Im
2
2

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DOI: 10.1039/C7DT02759A
b
a
a
b
1
15.66 (s, CHallyl), 115.39 (s, CHallyl), 61.20 (d, JCP = 3.8 Hz, CH2allyl), 59.95 (d, JCP = 2.5
b
a
b
a
Hz, CH2allyl), 57.43 (s, CH2allyl), 56.84 (s, CH2allyl), 52.85 (d, JCP = 20.1 Hz, NCH
2
), 52.74
b
a
b
a
(
d, JCP = 18.9 Hz, NCH
2
), 27.46 (s, CH
2
), 26.45 (s, CH
2
), 20.22 (s, CH3Mes), 20.19 (s,
a
b
b
a
b
CH3Mes), 17.34 (s, CH3Mes), 17.22 (s, CH3Mes), 17.17 (s, CH3Mes), 17.15 (s, CH3Mes), 3.18
a
+
+
(
d, JCP = 30.2 Hz, PCH), 2.52 (d, JCP = 31.4 Hz, PCH); MS (ES ): m/z: 635.5 [M – CF
3
SO
3
] .
Elemental analysis for C37
H, 4.83 N 4.05.
38 3 2 3
H F N O PPdS: calcd, C, 56.60 H, 4.88 N 3.57; found, C, 56.30
3
prop-1,3-diyl)-imidazol-2-yliden-chloro( -2-
1-methyl-3-(3-(triphenylphosphonio)
η
propen-1-yl)palladium(II) trifluoromethanesulfonate [12a,b](OTf)
A 1/1 mixture of tBuOK and complex [7a,b](OTf) (0.33 g, 0.46 mmol) in presence of
molecular sieves (4 Å) was cooled to –78°C and THF (10 mL) was added. The suspension
was warmed to room temperature and stirred for 2 hours. After evaporation of the solvent, the
2 2
solid residue was dissolved in CH Cl (10 mL) and filtered over celite. Purification by
chromatography on silica gel (AcOEt/MeOH) gave a yellow powder as a mixture of two
diastereoisomers [12a,b](OTf) (55/45) (0.22 g, 69%); (Mp = 82-84 °C). NMR assignment:
a
b
31
1
a
major isomer (55%); minor isomer (45%): P{ H} NMR (CD
3
CN, 25 °C):
δ
= +30.99 (s),
b
1
a,b
a
+
32.06 (s); H NMR (CD
3
CN, 25 °C):
δ
= 7.53-7.80 (m, 33.75H, CHPh), 7.09 (brs, 1.25H,
a
b
b
a,b
CHIm), 7.02 (brs, 1.25H, CHIm), 6.95 (brs, 1H, CHIm), 6.91 (brs, 1H, CHIm), 4.87-5.00 (m,
a,b
a,b
b
2
2 2
.25H, CHallyl), 4.01-4.17 (m, 2.25H, NCH ), 3.80-3.91 (m, 4.5H, NCH , CH2allyl), 3.61
a
a
b
(
s, 3H, NCH
3
), 3.53 (s, 3.75H, NCH
3
), 3.51-3.67 (m, 1.25H, NCH
2
), 2.96 (d, JHH = 7.4 Hz,
a
a,b
1
H, CH2allyl), 2.68 (d, JHH = 13.0 Hz, 1.25H, CH2allyl), 2.42-2.52 (m, 2.25H, CH
2
), 2.19-
a,b
a,b
a,b
b
2
2
.27 (m, 2.25H, CH2allyl), 1.95-2.00 (m, 2.25H, PCH), 1.51-1.76 (m, 2.25H, CH ), 1.47
1
3
1
a
(
d, JHH = 13.1 Hz, 1H, CH2allyl); C{ H} NMR (CD
3
CN, 25 °C):
δ
= 177.69 (s, N
2
C),
b
a
b
a,b
1
76.60 (s, N
2
C), 133.45 (d, JCP = 9.0 Hz, CHPh), 133.26 (d, JCP = 10.0 Hz, CHPh), 132.97
b
a
(
d, JCP = 3.0 Hz, CHPh), 129.15 (d, JCP = 13.1 Hz, CHPh), 129.03 (d, JCP = 11.1 Hz, CHPh),
b
a
a
a
1
25.24 (d, JCP = 83.5 Hz, CPh), 125.14 (d, JCP = 83.5 Hz, CPh), 121.54 (s, CHIm), 121.43 (s,
a,b
b
b
b
3
CHIm), 121.15 (q, JCF = 320.9 Hz, CF ), 121.02 (s, CHIm), 120.85 (s, CHIm), 117.29 (s,
a
a
b
b
a
CHallyl), 116.35 (s, CHallyl), 61.11 (s, CH2allyl), 59.31 (s, CH2allyl), 56.63 (s, CH2allyl), 55.04
a
b
b
(
s, CH2allyl), 53.08 (d, JCP = 18.1 Hz, NCH
2
), 52.74 (d, JCP = 19.1 Hz, NCH
2
), 37.73 (s,
a
a
b
a
NCH
3
), 37.63 (s, NCH
3
), 26.82 (s, CH
2
), 26.49 (s, CH
2
), 1.55 (d, JCP = 33.2 Hz, PCH),
b
+
+
1
.25 (d, JCP = 32.2 Hz, PCH); MS (ES ): m/z: 531.1 [M – CF
3
SO
3
] . Elemental analysis for
29 30 3 2 3
C H F N O PPdS: calcd, C, 51.15 H, 4.44 N 4.11; found, C, 50.85 H, 4.29 N 3.83.
2
3

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DOI: 10.1039/C7DT02759A
1-mesityl-3-(3-(triphenylphosphonio)
prop-1,3-diyl)-4,5-dihydro-imidazol-2-yliden-
3
chloro(
η
-2-propen-1-yl)palladium(II) trifluoromethanesulfonate [13a,b](OTf)
A 1/1 mixture of tBuOK and complex [8](OTf) (0.40 g, 0.48 mmol) in presence of molecular
sieves (4 Å) was cooled to –78°C and THF (10 mL) was added. The suspension was warmed
to room temperature and stirred for 2 hours. After evaporation of the solvent, the solid residue
2 2
was dissolved in CH Cl (10 mL) and filtered over celite. Purification by chromatography on
silica gel (AcOEt) gave a yellow powder as a mixture of two diastereoisomers [13a,b](OTf)
a
b
(
70/30) (0.30 g, 80%); (Mp = 102-104 °C). NMR assignment: major isomer (70%); minor
31
1
b
a
1
isomer (30%): P{ H} NMR (CD
3
CN, 25 °C):
δ
= +33.94 (s), +34.01 (s); H NMR
a,b
a,b
a,b
(
3
CD CN, 25 °C): δ = 7.70-7.76 and 7.58-7.63 (m, 48H, CHPh), 6.97-7.02 (brs, 6.4H,
a
b
a,b
CHMes), 4.51-4.62 (m, 2.2H, CHallyl), 4.19-4.29 (m, 1H, CHallyl), 3.78-4.02 (m, 13.8H,
a,b
a
NCH
2
, CH2Im), 3.40-3.56 (m, 5.4H, NCH
2
, CH2Im), 3.00 (d, JHH = 7.2 Hz, 2.2H, CH2allyl),
b
a
b
a
2
.68 (dd, JHH = 2.2, 7.3 Hz, 1H, CH2allyl), 2.39 (s, 6.6H, CH3Mes), 2.31 (s, 3H, CH3Mes), 2.27
b
b
a
(
s, 6.6H, CH3Mes), 2.26 (s, 3H, CH3Mes), 2.25 (s, 3H, CH3Mes), 2.23 (s, 6.6H, CH3Mes), 1.90-
a,b
b
a
2
.40 (m, 13.8H, CH2, CH2allyl, PCH), 1.44 (d, JHH = 13.1 Hz, 1H, CH2allyl), 1.14 (d, JHH
=
a
13
1
1
3.1 Hz, 2.2H, CH2allyl), 1.03 (d, JHH = 13.3 Hz, 2.2H, CH2allyl); C{ H} NMR (CD
3
CN, 25
a
b
b
°C):
δ
= 205.01 (d, JCP = 3.0 Hz, N
2
C), 203.89 (d, JCP = 2.0 Hz, N
2
C), 138.08 (s, CMes),
a
b
a
a
b
1
38.00 (s, CMes), 137.41 (s, CMes), 137.25 (s, CMes), 136.55 (s, CMes), 136.45 (s, CMes),
b
a
a
b
1
36.33 (s, CMes), 136.23 (s, CMes), 133.34 (d, JCP = 8.0 Hz, CHPh), 133.28 (d, JCP = 8.0 Hz,
b
a
b
CHPh), 133.18 (d, JCP = 3.0 Hz, CHPh), 133.12 (d, JCP = 3.0 Hz, CHPh), 129.25 (d, JCP = 12.1
a
b
a
a,b
Hz, CHPh), 129.21 (d, JCP = 12.1 Hz, CHPh), 129.06 (s, CHMes), 128.96 (s, CHMes), 128.88
b
a
a,b
(
s, CHMes), 125.22 (d, JCP = 82.5 Hz, CPh), 124.96 (d, JCP = 83.5 Hz, CPh), 121.10 (q, JCF
=
a,b
a
b
3
3
20.9 Hz, CF ), 115.87 (s, CHallyl), 63.19 (d, JCP = 4.0 Hz, CH2allyl), 61.43 (d, JCP = 4.0 Hz,
b
a
a
b
b
CH2allyl), 57.07 (s, CH2allyl), 56.05 (s, CH2allyl), 51.63 (s, CH2Im), 51.38 (s, CH2Im), 50.98
a
b
a
(
2 2
d, JCP = 17.1 Hz, NCH ), 50.61 (d, JCP = 16.1 Hz, NCH ), 50.44 (s, CH2Im), 50.01 (s,
b
a
b
a
a
CH2Im), 25.66 (s, CH
2
), 24.68 (s, CH
2
), 20.12 (s, CH3Mes), 20.07 (s, CH3Mes), 17.82 (s,
b
b
a
b
CH3Mes), 17.56 (s, CH3Mes), 17.25 (s, CH3Mes), 17.15 (s, CH3Mes), 2.45 (d, JCP = 31.2 Hz,
a
+
+
+
PCH), 2.37 (d, JCP = 32.2 Hz, PCH); MS (ES ): m/z: 637.2 [M – CF
calcd for PPd, 637.1978; found, 637.1987. Elemental analysis for
PPdS: calcd, C, 56.46 H, 5.12 N 3.56; found, C, 56.24 H, 5.13 N 3.54.
3 3
SO ] . HRMS (ES ):
36 40 2
C H N
37 40 3 2 3
C H F N O
2
4

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DOI: 10.1039/C7DT02759A
Single-crystal X-ray diffraction analyses of [1]Br
6](OTf), 9, 10, and [11a,b](OTf).
X-ray diffraction data collections were carried out on either a Bruker D8 / APEX II / Incoatec
IµS Microsource diffractometer ([1](OTf) , [2](OTf) , [5]Br, [6](OTf), 9, 10, and
11a,b](OTf)), or on a Agilent Gemini Xcalibur / EOS / enhanced X-ray source diffractometer
[1]Br , [3]Br ). All calculations were performed on a PC compatible computer using the
2 2 2 2
, [1](OTf) , [2](OTf) , [3]Br , [5]Br,
[
2
2
[
(
2
2
2
5
26
WinGX system. The structures were solved using the SIR92 program, which revealed in
each instance the position of most of the non-hydrogen atoms. All the remaining non-
hydrogen atoms were located by the usual combination of full matrix least-squares refinement
2
7
and difference electron density syntheses using the SHELX program. Atomic scattering
factors were taken from the usual tabulations. Anomalous dispersion terms for Rh, Pd, S, and
P atoms were included in Fc. All non-hydrogen atoms were allowed to vibrate anisotropically.
3 2 2
The hydrogen atoms were generally set in idealized positions (R CH, C–H = 0.96 Å; R CH ,
2
C–H = 0.97 Å; RCH
3
, C–H = 0.98 Å; C(sp )–H = 0.93 Å; Uiso 1.2 or 1.5 times greater than
the Ueq of the carbon atom to which the hydrogen atom is attached) and their positions refined
3
as “riding” atoms. The hydrogen atoms attached to the disordered η -allyl group in the
structure of [6](OTf), and [11a,b](OTf) could not be located from the Fourier difference maps
2
and they were not included in the refinements. The hydrogen atoms attached the sp carbon
atoms of the cod ligand in the structure of [5]Br were indeed located from a Fourier difference
2
map; their positions were refined with isotropic temperature factors arbitrarily set to 0.04 Å .
After completing the initial structure solutions for complexes [6](OTf), and [11a,b](OTf), it
was found that 8.5% and 10% of the total cell volumes, respectively, was filled with
disordered solvent molecules, which, however, could not be modeled in terms of discrete
molecules. The disordered solvents contributions in both structures were then substracted
2
8
from the observed data using the SQUEEZE procedure. CCDC 1558455-1558463 contain
the supplementary crystallographic data for the two structures unveiled in this paper. These
data can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
The authors thank the Centre National de la Recherche Scientifique (CNRS) for financial
support.
2
5

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DOI: 10.1039/C7DT02759A
Notes and references
1
2
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(a) S. Conejero, M. Song, D. Martin, Y. Canac, M. Soleilhavoup, G. Bertrand, Chem. Asian.
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7
In the acyclic series, phosphonio carbenes and their complexes have been reported to be
stable. For examples of phosphonio carbenes, see: (a) S. Conejero, Y. Canac, F. S. Tham, G.
Bertrand, Angew. Chem. Int. Ed. 2004, 43, 4089–4093; (b) Y. Canac, S. Conejero, M.
Soleilhavoup, B. Donnadieu, G. Bertrand, J. Am. Chem. Soc. 2006, 128, 459–464. For
examples of phosphonio carbene metal complexes, see: (c) D. A. Valyaev, N. Lugan, G.
Lavigne, N. A. Ustynyuk, Organometallics 2011, 30, 2318–2332; (d) D. A. Valyaev, S.
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2175–2178.
2
6

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8
(a) K. H. Shaughnessy, Chem. Rev. 2009, 109, 643–710; (b) D. J. M. Snelders, G. van
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Trans. 2011, 40, 2588–2600; (d) J. Klingele, Coord. Chem. Rev. 2015, 292, 15–29.
9
A 4-ammonio-substituted imidazolium salt has been recently prepared, where the
ammonium moiety was shown to modify the electronic properties of the corresponding NHC,
see: M. Ruamps, N. Lugan, V. César, Organometallics 2017, 36, 1049–1055.
10 G. Wittig, G. Geissler, Liebigs Ann. Chem. 1953, 580, 44–57.
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Abdellah, N. Debono, Y. Canac, C. Duhayon, R. Chauvin, Dalton Trans. 2009, 38, 7196–
7
1
1
1
2
1
1
1
1
1
202; (c) Y. Canac, R. Chauvin, Eur. J. Inorg. Chem. 2010, 2325–2335.
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30, 8406–8413; (b) Y. Canac, C. Lepetit, Inorg. Chem. 2017, 56, 667–675.
3 A. J. Arduengo, III, Jr. F. P. Gentry, P. K. Taverkere, H. E. Howard, III, US Patent 6,
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4 C. Marshall, M. F. Ward, J. M. S. Skakle, Synthesis 2006, 6, 1040–1044.
5 S. O. Grim, E. F. Davidoff, T. J. Marks, Z. Naturforsch 1971, 26 b, 184–190.
6 CCDC 1558455 [1]Br , CCDC 1558456 [1](OTf) , CCDC 1558457 [2](OTf) , CCDC
2
2
2
558458 [3]Br , CCDC 1558459 [5]Br, CCDC 1558460 9, CCDC 1558461 10, CCDC
2
558462 [6](OTf), and CCDC 1558463 [11a,b](OTf) contain the supplementary
crystallographic data for this paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
1
7 For pK values, see: http://evans.rc.fas.harvard.edu/pdf/evans_pKa_table.pdf.
a
18 (a) E. E. Schweizer, R. D. Bach, J. Org. Chem. 1964, 29, 1746–1751; (b) T. A. Albright,
W. J. Freeman, E. E. Schweizer, J. Am. Chem. Soc. 1975, 97, 2946–2950.
9 The use of a stoichiometric amount of Ag O results in the partial conversion of
1
2
imidazolium salt [1]Br into Ag(I) complex 9.
2
2
0 (a) P. de Frémont, N. M. Scott, E. D. Stevens, T. Ramnial, O. C. Lightbody, C. L. B.
Macdonald, J. A. C. Clyburne, C. D. Abernethy, S. P. Nolan, Organometallics 2005, 24,
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Lin, C. S. Vasan, Coord. Chem. Rev. 2007, 251, 642–670.
6
4
-
2
1 The related non coordinating anion (Ag Br ) has been reported to neutralize different
4 8
cations, see; (a) S. C. Chen, H. H. Hsueh, C. H. Chen, C. S. Lee, F. C. Liu, I. J. B. Lin, G. H.
2
7

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Inorg. Chem. 2011, 30, 2574–2577.
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23 P. A. Byrne, D. G. Gilheany, Chem. Eur. J. 2016, 22, 9140–9154.
24 Attempts to isolate a NHC-phosphonium ylide Rh(I) complex from [5]Br led to a mixture
of unidentified products.
2
2
4
2
2
5 L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837–838.
6 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 1994, 27,
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7
G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112–122.
8 P. v. d. Sluis, A. L. Spek, Acta Crystallogr. 1990, A46, 194–201.
Graphical Abstract
NHC Pd(II) complexes featuring a propyl bridge were ionized by the introduction of a
phosphonium moiety, which may coordinate to the metal center or remain pendant.
2
8